libstdc++: Add nonnull to starts_with/ends_with/contains string members

Ideally this wouldn't be needed, because eventually these pointers all
get passed to either the basic_string_view(const CharT*) constructor, or
to basic_string_view::find(const CharT*), both of which already have the
attribute. But for that to work requires optimization, so that the null
value gets propagated through the call chain.

Adding it explicitly to each member that requires a non-null pointer
makes the diagnostics more reliable even without optimization. It's
better to give a diagnostic earlier anyway, at the actual problematic
call in the user's code.

libstdc++-v3/ChangeLog:

	* include/bits/basic_string.h (starts_with, ends_with, contains):
	Add nonnull attribute.
	* include/bits/cow_string.h (starts_with, ends_with, contains):
	Likewise.
	* include/std/string_view (starts_with, ends_with, contains):
	Likewise.
	* testsuite/21_strings/basic_string/operations/contains/nonnull.cc
	* testsuite/21_strings/basic_string/operations/ends_with/nonnull.cc
	* testsuite/21_strings/basic_string/operations/starts_with/nonnull.cc
	* testsuite/21_strings/basic_string_view/operations/contains/nonnull.cc
	* testsuite/21_strings/basic_string_view/operations/ends_with/nonnull.cc
	* testsuite/21_strings/basic_string_view/operations/starts_with/nonnull.cc

9 files changed, 81 insertions, 0 deletions

diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index b04fba9..9d8b415 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -3400,6 +3400,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       starts_with(_CharT __x) const noexcept
       { return __sv_type(this->data(), this->size()).starts_with(__x); }
 
+      [[__gnu__::__nonnull__]]
       constexpr bool
       starts_with(const _CharT* __x) const noexcept
       { return __sv_type(this->data(), this->size()).starts_with(__x); }
@@ -3412,6 +3413,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       ends_with(_CharT __x) const noexcept
       { return __sv_type(this->data(), this->size()).ends_with(__x); }
 
+      [[__gnu__::__nonnull__]]
       constexpr bool
       ends_with(const _CharT* __x) const noexcept
       { return __sv_type(this->data(), this->size()).ends_with(__x); }
@@ -3426,6 +3428,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       contains(_CharT __x) const noexcept
       { return __sv_type(this->data(), this->size()).contains(__x); }
 
+      [[__gnu__::__nonnull__]]
       constexpr bool
       contains(const _CharT* __x) const noexcept
       { return __sv_type(this->data(), this->size()).contains(__x); }
diff --git a/libstdc++-v3/include/bits/cow_string.h b/libstdc++-v3/include/bits/cow_string.h
index f16e33a..f5f0333 100644
--- a/libstdc++-v3/include/bits/cow_string.h
+++ b/libstdc++-v3/include/bits/cow_string.h
@@ -3012,6 +3012,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       starts_with(_CharT __x) const noexcept
       { return __sv_type(this->data(), this->size()).starts_with(__x); }
 
+      [[__gnu__::__nonnull__]]
       bool
       starts_with(const _CharT* __x) const noexcept
       { return __sv_type(this->data(), this->size()).starts_with(__x); }
@@ -3024,6 +3025,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       ends_with(_CharT __x) const noexcept
       { return __sv_type(this->data(), this->size()).ends_with(__x); }
 
+      [[__gnu__::__nonnull__]]
       bool
       ends_with(const _CharT* __x) const noexcept
       { return __sv_type(this->data(), this->size()).ends_with(__x); }
@@ -3038,6 +3040,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       contains(_CharT __x) const noexcept
       { return __sv_type(this->data(), this->size()).contains(__x); }
 
+      [[__gnu__::__nonnull__]]
       bool
       contains(const _CharT* __x) const noexcept
       { return __sv_type(this->data(), this->size()).contains(__x); }
diff --git a/libstdc++-v3/include/std/string_view b/libstdc++-v3/include/std/string_view
index 30ff136..5b96ffe 100644
--- a/libstdc++-v3/include/std/string_view
+++ b/libstdc++-v3/include/std/string_view
@@ -360,6 +360,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       starts_with(_CharT __x) const noexcept
       { return !this->empty() && traits_type::eq(this->front(), __x); }
 
+      [[__gnu__::__nonnull__]]
       constexpr bool
       starts_with(const _CharT* __x) const noexcept
       { return this->starts_with(basic_string_view(__x)); }
@@ -377,6 +378,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       ends_with(_CharT __x) const noexcept
       { return !this->empty() && traits_type::eq(this->back(), __x); }
 
+      [[__gnu__::__nonnull__]]
       constexpr bool
       ends_with(const _CharT* __x) const noexcept
       { return this->ends_with(basic_string_view(__x)); }
@@ -392,6 +394,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       contains(_CharT __x) const noexcept
       { return this->find(__x) != npos; }
 
+      [[__gnu__::__nonnull__]]
       constexpr bool
       contains(const _CharT* __x) const noexcept
       { return this->find(__x) != npos; }
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/operations/contains/nonnull.cc b/libstdc++-v3/testsuite/21_strings/basic_string/operations/contains/nonnull.cc
new file mode 100644
index 0000000..e987cb7
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/operations/contains/nonnull.cc
@@ -0,0 +1,12 @@
+// { dg-options "-std=gnu++23 -Wnonnull -O0" }
+// { dg-do compile { target c++23 } }
+
+#include <string>
+
+void
+test01(const std::string& s)
+{
+  s.contains((const char*)nullptr);  // { dg-warning "\\\[-Wnonnull" }
+  s.contains((char*)nullptr);	     // { dg-warning "\\\[-Wnonnull" }
+  s.contains(nullptr);		     // { dg-warning "\\\[-Wnonnull" }
+}
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/operations/ends_with/nonnull.cc b/libstdc++-v3/testsuite/21_strings/basic_string/operations/ends_with/nonnull.cc
new file mode 100644
index 0000000..1f2a156
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/operations/ends_with/nonnull.cc
@@ -0,0 +1,12 @@
+// { dg-options "-std=gnu++20 -Wnonnull -O0" }
+// { dg-do compile { target c++20 } }
+
+#include <string>
+
+void
+test01(const std::string& s)
+{
+  s.ends_with((const char*)nullptr);  // { dg-warning "\\\[-Wnonnull" }
+  s.ends_with((char*)nullptr);	      // { dg-warning "\\\[-Wnonnull" }
+  s.ends_with(nullptr);		      // { dg-warning "\\\[-Wnonnull" }
+}
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/operations/starts_with/nonnull.cc b/libstdc++-v3/testsuite/21_strings/basic_string/operations/starts_with/nonnull.cc
new file mode 100644
index 0000000..8514359
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/operations/starts_with/nonnull.cc
@@ -0,0 +1,12 @@
+// { dg-options "-std=gnu++20 -Wnonnull -O0" }
+// { dg-do compile { target c++20 } }
+
+#include <string>
+
+void
+test01(const std::string& s)
+{
+  s.starts_with((const char*)nullptr);  // { dg-warning "\\\[-Wnonnull" }
+  s.starts_with((char*)nullptr);	// { dg-warning "\\\[-Wnonnull" }
+  s.starts_with(nullptr);		// { dg-warning "\\\[-Wnonnull" }
+}
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/contains/nonnull.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/contains/nonnull.cc
new file mode 100644
index 0000000..c0d274f
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/contains/nonnull.cc
@@ -0,0 +1,12 @@
+// { dg-options "-std=gnu++23 -Wnonnull -O0" }
+// { dg-do compile { target c++23 } }
+
+#include <string_view>
+
+void
+test01(std::string_view s)
+{
+  s.contains((const char*)nullptr);  // { dg-warning "\\\[-Wnonnull" }
+  s.contains((char*)nullptr);	     // { dg-warning "\\\[-Wnonnull" }
+  s.contains(nullptr);		     // { dg-warning "\\\[-Wnonnull" }
+}
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/ends_with/nonnull.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/ends_with/nonnull.cc
new file mode 100644
index 0000000..09a9997
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/ends_with/nonnull.cc
@@ -0,0 +1,12 @@
+// { dg-options "-std=gnu++20 -Wnonnull -O0" }
+// { dg-do compile { target c++20 } }
+
+#include <string_view>
+
+void
+test01(std::string_view s)
+{
+  s.ends_with((const char*)nullptr);  // { dg-warning "\\\[-Wnonnull" }
+  s.ends_with((char*)nullptr);	      // { dg-warning "\\\[-Wnonnull" }
+  s.ends_with(nullptr);		      // { dg-warning "\\\[-Wnonnull" }
+}
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/starts_with/nonnull.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/starts_with/nonnull.cc
new file mode 100644
index 0000000..c47f1da
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/starts_with/nonnull.cc
@@ -0,0 +1,12 @@
+// { dg-options "-std=gnu++20 -Wnonnull -O0" }
+// { dg-do compile { target c++20 } }
+
+#include <string_view>
+
+void
+test01(std::string_view s)
+{
+  s.starts_with((const char*)nullptr);  // { dg-warning "\\\[-Wnonnull" }
+  s.starts_with((char*)nullptr);	// { dg-warning "\\\[-Wnonnull" }
+  s.starts_with(nullptr);		// { dg-warning "\\\[-Wnonnull" }
+}